Although a Rule could be implemented with a consequence that sends a larger aroundRadius value as a query parameter, the condition for that rule cannot be based on the number of results/hits that the query returns.
Though this would require coding logic outside of Algolia, one possible solution might be to implement a logical check for a low number of results from the first query with the smaller radius (ie:if (hits < 10)).
If the condition is met, your site could then automatically trigger a second query with the larger radius.